The invention relates to apparatus responsive to a light-affecting substance in a fluid such as, for example, oil mist in an atmosphere. An embodiment of the inventon to be described is a detector for detecting lubricating oil mist of excessive concentration occurring during the running of rotating plant and machinery and especially for detecting such mists in the crank cases of internal combustion engines including diesel engines. Excessive oil mist formation may constitute an explosion hazard and it is clearly advantageous to be able to detect, at an early stage, such excessive oil mist formations. Excessive oil mist formation in crankcases may occur as a result of overheating or wear of mechanical parts, and means for detecting such excessive oil mist formations also enables early remedial action to be taken to prevent further damage.
However, the invention is also applicable to the detection of other light affecting substances and to the detection of mist in general, for example, the detection of vapour mists in air conditioning, refrigerating and gas cooling systems. Detection of colourless mists is possible by, for example, passing the mist over an appropriate chemical which will react to colour the mist. Furthermore, the densities of exhaust gases from internal combustion engines can be measured.
Arrangements are known in which samples of fluids are taken sequentially using a mechanical rotary valve, and the presence of light-affecting substances in each sample then detected photo-electrically. Such arrangements are slow and cumbersome.
An object of the invention is to provide improved apparatus responsive to light-affecting substances in a fluid.
A more specific object is to provide such apparatus capable of operating at high speed so as to enable a number of samples to be taken and measured individually within a very short total cycle time.